The installer for Windows checks the version of the DLL if it is present. If it is a pre InterBase 6.0 version dll a warning message is displayed during the install. It may be possible to continue successfully with an old dll, however you may experience problems either during the install process when the driver is added to the list of drivers, or in latter use of the driver.
If this happens then it will be necessary to install a later version of the DLL.